Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 20 2023 20:02:15 ACUS01 KWNS 202002 SWODY1 SPC AC 202000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0200 PM CST Mon Nov 20 2023 Valid 202000Z - 211200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF NORTHERN/CENTRAL LA TO CENTRAL/SOUTHERN MS... ....SUMMARY... Tornadoes, at least a couple of which should be strong, scattered to numerous damaging thunderstorm winds, and isolated large hail are expected through tonight, centered on parts of Louisiana across Mississippi. ....Lower MS Valley... Overall severe threat area appears increasingly focused within a messy, complex mode across the LA/MS region. Initial supercells across the Sabine Valley, embedded within a broader convective cluster that is driven by a low-level warm conveyor, should spread towards the Lower MS Valley. These will likely strengthen in tandem with increasing boundary-layer moisture from the central Gulf Coast. The relative greatest tornado potential may evolve along the southern corridor of sustained, semi-discrete supercells coincident with the apex of upper 60s surface dew points. The Fort Polk, LA VWP has sampled a steady increase in 0-3 km SRH over the past few hours, and the prior level 3-Enhanced Risk likely captures the greatest threat corridor for at least a couple strong tornadoes. Primary changes with this outlook are to trim the western extent behind the cold front and lower severe probabilities where low-level flow has veered ahead of the front, as well as to lower probabilities over the Mid-South region where the northern extent of the surface warm front has struggled to advance amid pervasive rainfall/stratus. ...Grams.. 11/20/2023 ..PREV DISCUSSION... /ISSUED 1026 AM CST Mon Nov 20 2023/ ....East Texas into the Lower Mississippi Valley and Central Gulf Coast... A positively tilted upper trough over the southern/central Plains will progress slowly eastward through the period across the lower and mid MS Valley, while transitioning to a closed mid/upper-level low. At the surface, a weak low centered over southern/central OK this morning is forecast to develop across northeast TX and towards the ArkLaMiss by this evening. An associated warm front will continue to lift/mix northward through tonight across east TX into the lower MS Valley. A cold front attendant to the surface low will also sweep eastward over these regions through the period. Low-level moisture return is ongoing in earnest this morning across east TX into the lower MS Valley, with at least low 60s surface dewpoints becoming prevalent across the warm sector along and south of the diffuse warm front. Most guidance suggests that mid to perhaps upper 60s surface dewpoints will become more common by late this afternoon from far east TX into parts of southern/central LA/MS. Large-scale ascent associated with the mid/upper-level trough and increasing low-level warm advection associated with a gradually strengthening southerly low-level jet will both aid in the development of surface-based convection by early afternoon. Initial development will likely emanate from bands of elevated low-level warm-advection driven showers/thunderstorms ongoing across central into east TX. Rather strong deep-layer shear of 50-60+ kt will easily support supercells with this initial activity. Around 500-1250 J/kg of MLCAPE should also be present with continued diurnal heating of the moistening low-level airmass, which will support surface-based thunderstorms as this convection spreads into LA this afternoon and early evening. Large hail may be a concern with any supercell that can be sustained. But, the tornado potential is expected to gradually increase this afternoon and evening from parts of far east TX into northern/central LA and southern/central MS as a southerly low-level jet strengthens to around 35-40 kt. Favorable low-level shear and the best chance for several tornadoes will likely be maximized along/near the warm front this evening and tonight, with ample curvature noted in the 0-1 km layer from various NAM/RAP forecast hodographs. No changes have been made to the Enhanced Risk, which still seems to capture the best corridor of strong tornado potential and scattered to possibly numerous damaging wind gusts. Cell mergers and some upscale growth seems likely this evening and overnight across the lower MS Valley. Line-embedded low-level circulations should still pose a threat for QLCS tornadoes as one or more clusters/lines advances eastward across MS and western AL late tonight through early Tuesday morning in a weakly unstable but strongly sheared environment. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .